It is typical in hydrocarbon wells to “set” or actuate a downhole tool, such as packers, bridge plugs, high-expansion gauge hangers, straddles, wellhead plugs, cement retainers, through-tubing plugs, etc. Some of these downhole tools are set to selectively seal a fluid pathway, such as a wellbore annulus defined between the wellbore and tubing string or the primary through-bore of the string. These tools are run-in and in some cases retrieved using various conveyance methods such as a wireline, slickline, or coiled tubing. The DFG unit is often retrieved after setting the downhole tool. The DFG unit used for setting tools can be mechanically, electrically, chemically, explosively, hydraulically, electro-mechanically or otherwise powered. One type of DFG uses electro-mechanical power, where the DFG converts electrical power, typically provided by a battery unit, into mechanical movement, typically rotary or longitudinal movement of a shaft or power rod. One such setting tool is the DPU (trade name) Downhole Power Unit available from Halliburton Energy Services, Inc. Disclosure relating to DFG units, their operation and construction can be found in the following, which are each incorporated herein for all purposes: U.S. Pat. No. 7,051,810 to Clemens, filed Sep. 15, 2003; U.S. Pat. No. 7,367,397 to Clemens, filed Jan. 5, 2006; U.S. Pat. No. 7,467,661 to Gordon, filed Jun. 1, 2006; U.S. Pat. No. 7,000,705 to Baker, filed Sep. 3, 2003; U.S. Pat. No. 7,891,432 to Assal, filed Feb. 26, 2008; U.S. Patent Application Publication No. 2011/0168403 to Patel, filed Jan. 7, 2011; U.S. Patent Application Publication Nos. 2011/0073328 to Clemens, filed Sep. 23, 2010; 2011/0073329 to Clemens, filed Sep. 23, 2010; 2011/0073310 to Clemens, filed Sep. 23, 2010.
Electro-mechanical DFG setting tools are commonly available and can be purchased in various sizes, including various stroke lengths. While most downhole tools require a relatively short stroke to set, other downhole tools require a longer stroke than is typically available from an electro-mechanical DFG. Additionally, electro-mechanical DFG setting tools tend to have a relatively slower setting speed, resulting in longer setting times. Consequently, there is a need for methods and apparatus for improved electro-mechanical downhole force generators having a relatively longer setting stroke and a relatively quicker setting speed for use with downhole tools.